Focal plane arrays (FPAs) are two-dimensional arrays of photodetectors disposed in the focal plane of a lens for imaging, spectrometry, lidar, wave-front sensing, and other applications. Conventional FPAs typically provide analog readouts, with the analog signals generated at the pixel level converted to digital signals by external analog-to-digital converters (ADCs). Once converted by the external ADCs, the digital signals may be processed according to the demands of a particular application.
Fundamental limitations on the photodetector dynamic range, active area, and readout noise floor limit the practical scalability of conventional FPAs. For example, decreasing the size of capacitors used to store accumulated photocurrents causes the data transfer rate (also known as the frame rate) to increase beyond acceptable limits. Similarly, electronics noise and ringing limit the amount of data that can be transmitted on a single output tap to maintain the desired signal-to-noise ratio (SNR) and dynamic range. Attempting to scale conventional analog technology to meet more demanding performance requirements leads to an FPA that is significantly large and complex, and consumes excessive power for most applications.